Most of the writing effort in ages before mechanised printing went into replication. We know more about the scribes and copyists of the ancient and medieval world than about the authors themselves. Sometimes, the scribe was the author and the author was the scribe. But most of the time, the scribe didn’t know the author or the book they were copying. They often made mistakes because they didn’t know. And their mistakes encouraged others to make even more. Scribal mistakes, misattributions, unwarranted additions and the like were an author’s worse nightmare
But they are also the historian’s glittering dream.
The paradox in the pre-modern history of books is that errors are preferable to the absence of errors. Errors are traces, allowing us to see the turns and twists a written work takes before it gets to us, or at least to an error-free mechanicised culture of writing. Scribes are not unlike spies. They remain undercover until they make a mistake, whereupon their profile gets hot and we can see them.
Bouncing from one error to another, we pick up the thread and connect the dots. And we get the big picture of the main road by identifying all the instances that the scribes went off-road. But that is not to say that sometimes the off-roads lead to previously unsuspected main roads. Until the whole landscape gets mapped out, however criss-crossed it may be.